Evaluation of Nitric Oxide Removal from Simulated Flue Gas by Fe(II)EDTA/Fe(II)citrate Mixed Absorbents

Abstract

Fe(II)EDTA is an effective absorbent for the integrated chemical absorption–biological reduction system in removing nitric oxide (NO) from flue gas. However, this absorbent is subject to some defects, such as oxidation by oxygen. In order to overcome this drawback, instead of using Fe(II)EDTA solely, a mixed absorbent containing both Fe(II)EDTA and Fe(II)Cit (Cit = citrate) is employed to absorb NO from simulated flue gas. The mixed absorbent not only shows a high NO absorption capacity similar to a Fe(II)EDTA absorbent, but also exhibits high NO absorption rate and good resistance to oxidation in simulated flue gas. This mixed absorbent can maintain 80% NO removal efficiency at 323 K for more than two hours at an inlet NO concentration of 670 mg·m–3, which is almost as effective as the Fe(II)EDTA absorbent at the same Fe(II) concentration. The oxidation rate constant of Fe(II) in the mixed absorbent is also slower than that in the Fe(II)EDTA absorbent. The optimal molar ratio of Fe(II)Cit to Fe(II)EDTA in the mixed absorbent was found to be 3:1. The effects of several key factors for NO removal, such as the inlet concentrations of NO (200–670 mg·m–3), O2 (1–6.5%), and SO32– (0–43 mg·L–1) and the pH of the mixed absorbent, have been studied. Interestingly, results seem to suggest that SO32– is beneficial for the removal of NO in the system. These findings provide fundamental data for the design of NO removal system for industrial applications with mixed Fe(II)EDTA/Fe(II)Cit absorbent.